Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0043346 (xeroderma pigmentosum)
 2,924 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To study the effect of nucleotide excision repair on the spectrum of mutations induced in diploid human fibroblasts by UV light (wavelength, 254 nm), we synchronized repair-proficient cells and irradiated them when the HPRT gene was about to be replicated (early S phase) so that there would be no time for repair in that gene before replication, or in G1 phase 6 h prior to S, and determined the kinds and location of mutations in that gene. As a control, we also compared the spectra of mutations induced in synchronized populations of xeroderma pigmentosum cells (XP12BE cells, which are unable to excise UV-induced DNA damage). Among the 84 mutants sequenced, base substitutions predominated. Of the XP mutants from S or G1 and the repair-proficient mutants from S, approximately 62% were G.C----A.T. In the repair-proficient mutants from G1, 47% were. In mutants from the repair-proficient cells irradiated in S, 71% (10 of 14) of the premutagenic lesions were located in the transcribed strand; with mutants from such cells irradiated in G1, only 20% (3 of 15) were. In contrast, there was no statistically significant difference in the fraction of premutagenic lesions located in the transcribed strand of the XP12BE cells; approximately 75% (24 of 32) of the premutagenic lesions were located in that strand, i.e., 15 of 19 (79%) in the S-phase cells and 9 of 13 (69%) in the G1-phase cells. The switch in strand bias supports preferential nucleotide excision repair of UV-induced damage in the transcribed strand of the HPRT gene.
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PMID:Cell cycle-dependent strand bias for UV-induced mutations in the transcribed strand of excision repair-proficient human fibroblasts but not in repair-deficient cells. 200 88

Human cells deficient in rate of excision repair of DNA damage induced by UV-radiation, i.e., xeroderma pigmentosum (XP) cells, are much more sensitive to the mutagenic effect of UV than are cells from normal persons. The lower frequency of mutants in the latter cells has been attributed to the fact that, unlike XP cells, they excise most of the potentially mutagenic lesions before these can be converted into mutations. If semi-conservative DNA synthesis on a template still containing unexcised lesions is responsible for introducing mutations and if replication of the gene of interest, e.g., hypoxanthine (guanine)phosphoribosyltransferase (HPRT) for thioguanine resistance or the elongation factor 2 (EF-2) for diphtheria toxin resistance, occurs at a particular time during S-phase, it should be possible to shorten the time available for such repair by synchronizing cells and irradiating them just as the gene is to be replicated. The predicted result would be a much higher frequency of mutants at one part in the S-phase than at other times. To test this, cells were synchronized using the alpha-polymerase inhibitor aphidicolin, which blocks cells at the G1/S border. Autoradiography, cytofluorimetry, and incorporation of tritiated thymidine studies showed that DNA synthesis started immediately after release from aphidicolin and was completed in 8-10 h. Cells irradiated with 6 J/m2 at various times post-release were assayed for survival and mutations. The frequency of thioguanine- or diphtheria toxin-resistant cells in the population was highest in cells irradiated during the first fifth of the S-phase, i.e., 0-1.5 h post-release. It was significantly lower in cells irradiated at later times. In contrast, UV-induced cytotoxicity showed no significant time dependence during S-phase. These data suggest that the HPRT and EF-2 genes are replicated early in S-phase.
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PMID:The frequency of mutants in human fibroblasts UV-irradiated at various times during S-phase suggests that genes for thioguanine- and diphtheria toxin-resistance are replicated early. 393 Sep 56

Excision repair deficiencies in groups A and G xeroderma pigmentosum (XP) cells are transiently complemented after microinjection of HeLa poly(A)+RNA, but those in groups D and F are not complemented (Legerski et al., 1984). We tested XP cells belonging to the seven complementation groups, A-G, and Cockayne's syndrome (CS) cells belonging to the two complementation groups, A and B, for transient correction by microinjection of total poly(A)+RNA from HeLa cells. Among the XP cells, unscheduled DNA synthesis (UDS) was increased only in XP-A cells by microinjection of total poly(A)+RNA. However, UDS was increased in XP-E and XP-G cells as well as in XP-A cells by microinjection of concentrated poly(A)+RNA fractionated on a 5-25% sucrose density gradient containing methylmercuric hydroxide. The sizes of XP-E and XP-G mRNA were estimated to be 1.5-2.7 kb and 2.0-3.8 kb, respectively, by comparison to internal marker RNAs including 18S rRNA, 28S rRNA, HPRT mRNA and XPAC mRNA. RNA synthesis recovery after UV exposure in CS cells was not increased by microinjection of either total poly(A)+RNA or fractionated RNA. These results provide estimates of the sizes of XP-E and XP-G proteins and will facilitate molecular cloning of DNA repair genes, especially of XP-E and XP-G genes.
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PMID:Complementation of xeroderma pigmentosum cells by microinjection of mRNA fractionated under denaturing conditions: an estimation of sizes of XP-E and XP-G mRNA. 750 87

Xeroderma pigmentosum (XP) variant patients are genetically predisposed to sunlight-induced skin cancer. Fibroblasts derived from these patients are extremely sensitive to the mutagenic effect of UV radiation and are abnormally slow in replicating DNA containing UV-induced photoproducts. However, unlike cells from the majority of XP patients, XP variant cells have a normal or nearly normal rate of nucleotide excision repair of such damage. To determine whether their UV hypermutability reflected a slower rate of excision of photoproducts specifically during early S phase when the target gene for mutations, i.e., the hypoxanthine (guanine) phosphoribosyltransferase gene (HPRT), is replicated, we synchronized diploid populations of normal and XP variant fibroblasts, irradiated them in early S phase, and compared the rate of loss of cyclobutane pyrimidine dimers and 6-4 pyrimidine-pyrimidones from DNA during S phase. There was no difference. Both removed 94% of the 6-4 pyrimidine-pyrimidones within 8 h and 40% of the dimers within 11 h. There was also no difference between the two cell lines in the rate of repair during G1 phase. To determine whether the hypermutability resulted from abnormal error-prone replication of DNA containing photoproducts, we determined the spectra of mutations induced in the coding region of the HPRT gene of XP variant cells irradiated in early S and G1 phases and compared with those found in normal cells. The majority of the mutations in both types of cells were base substitutions, but the two types of cells differed significantly from each other in the kinds of substitutions, but the two types differed significantly from each other in the kinds of substitutions observed either in mutants from S phase (P < 0.01) or from G1 phase (P = 0.03). In the variant cells, the substitutions were mainly transversions (58% in S, 73% in G1). In the normal cells irradiated in S, the majority of the substitutions were G.C --> A.T, and most involved CC photoproducts in the transcribed strand. In the variant cells irradiated in S, substitutions involving cytosine in the transcribed strand were G.C --> T.A transversions exclusively. G.C --> A.T transitions made up a much smaller fraction of the substitutions than in normal cells (P < 0.02), and all of them involved photoproducts located in the nontranscribed strand. The data strongly suggest that XP variant cells are much less likely than normal cells to incorporate either dAMP or dGMP opposite the pyrimidines involved in photoproducts. This would account for their significantly higher frequency of mutants and might explain their abnormal delay in replicating a UV-damaged template.
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PMID:Evidence from mutation spectra that the UV hypermutability of xeroderma pigmentosum variant cells reflects abnormal, error-prone replication on a template containing photoproducts. 832 Dec 29

We have characterized six SV40-transformed xeroderma pigmentosum cell lines (XP20S and XP12BE derived from female donors, XP12RO-SV, XP3BR/12SV, XP4PA-SV and XP8CAC-SV from male donors) for their usability in HPRT mutation studies. All cell lines exhibit hypersensitivity, compared with MRC5CV1 cells, towards the cytotoxic action of UV-irradiation. They were all shown to be heteronuclear and hyperdiploid with pronounced variability in chromosome number. Fluorescence in situ hybridization (FISH) with an X-chromosomal library (X-chromosome painting) and BrdUrd-labelling of late-replicating X-chromosomes demonstrated the presence of variable numbers of X-chromosomes and additional X-chromosomal material and suggested the presence of more than one genetically active HPRT allele in the majority of cells of five cell lines. The cell line XP8CAC-SV (complementation group C) seemed to be most suitable for HPRT mutation studies due to its near-diploid karyotype with only one X-chromosome in the majority of cells. From this cell line, a clonal subline was established (XP8CAC-SV-C1) which revealed the same UV-hypersensitivity as the parental cell line and a near-diploid karyotype with one X-chromosome in 94% of the metaphases. Molecular analysis of the HPRT gene gave a normal PCR amplification pattern for all exons and the normal wild-type sequence of the cDNA. HPRT tests with (+)-anti-benzo[a]pyrene-7,8-diol-9,10-oxide [(+)-anti-BPDE] showed a reproducible, concentration related increase in mutant frequencies. Compared with results with MRC5CV1 cells, the obtained data indicate spontaneous and (+)-anti-BPDE-induced hypermutability of the XP line. XP8CAC-SV-C1 thus represents a permanent XP cell line with characteristic cellular XP features which is convenient for studying the influence of deficient excision repair on HPRT mutant frequencies and mutation spectra.
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PMID:Characterization of SV40-transformed xeroderma pigmentosum cell lines for their usability in HPRT mutation studies. 937 20

Validity of measurement of somatic cell mutation frequency (Mf) at the hprt locus for evaluating cancer risk of the given individual was determined in pediatric patients. Peripheral lymphocytes (PL) from patients with various diseases, including acute lymphoblastic leukemia (ALL) and Hodgkin's disease (HD), DNA repair deficient syndromes or short stature receiving growth hormone (GH), were isolated through Ficoll-Hypaque sedimentation with informed consent. Mf at the hprt locus of PL was determined by limiting dilution assay using 6-thioguanine (6-TG). Results were as follows. (1) ALL patients after chemotherapy had higher Mf than that of age-matched controls. (2) Patients with HD tended to have higher Mf after chemotherapy. (3) Among DNA-repair deficient syndromes, diseases which are susceptible to cancer (Xeroderma pigmentosum, Ataxia telangiectasia) have high Mf, but those without any cancer disposition (Cockayne syndrome, Rothmund-Thomson syndrome) have normal Mf. (4) GH-receiving patients have normal Mf, regardless of total doses of GH. Measurement of Mf at HPRT locus may be useful for evaluating cancer risk of pediatric patients.
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PMID:Measurement of mutation frequency at the HPRT locus in peripheral lymphocytes. Is this a good method to evaluate a cancer risk in pediatric patients? 959 52

Homozygous loss of activity at the breast cancerpredisposing genes BRCA1 and BRCA2 (FANCD1) confers increased susceptibility to DNA double strand breaks, but this genotype occurs only in the tumor itself, following loss of heterozygosity at one of these loci. Thus, if these genes play a role in tumor etiology as opposed to tumor progression, they must manifest a heterozygous phenotype at the cellular level. To investigate the potential consequences of somatic heterozygosity for a BRCA1 mutation demonstrably associated with breast carcinogenesis on background somatic mutational burden, we applied the two standard assays of in vivo human somatic mutation to blood samples from a manifesting carrier of the Q1200X mutation in BRCA1 whose tumor was uniquely ascertained through an MRI screening study. The patient had an allele-loss mutation frequency of 19.4 x 10(-6) at the autosomal GPA locus in erythrocytes and 17.1 x 10(-6) at the X-linked HPRT locus in lymphocytes. Both of these mutation frequencies are significantly higher than expected from age-matched disease-free controls (P < 0.05). Mutation at the HPRT locus was similarly elevated in lymphoblastoid cell lines established from three other BRCA1 mutation carriers with breast cancer. Our patient's GPA mutation frequency is below the level established for diagnosis of homozygous Fanconi anemia patients, but consistent with data from obligate heterozygotes. The increased HPRT mutation frequency is more reminiscent of data from patients with xeroderma pigmentosum, a disease characterized by UV sensitivity and deficiency in the nucleotide excision pathway of DNA repair. Therefore, this BRCA1-associated breast cancer patient manifests a unique phenotype of increased background mutagenesis that likely contributed to the development of her disease independent of loss of heterozygosity at the susceptibility locus.
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PMID:Elevated levels of somatic mutation in a manifesting BRCA1 mutation carrier. 1815 61

We used padlock probes to study the rate of gene specific repair of three genes, OGG1 (8-oxoguanine-DNA glycosylase-1), XPD (xeroderma pigmentosum group D), and HPRT (hypoxanthine-guanine phosphoribosyltransferase) in human lymphocytes, in relation to the repair rate of Alu repeats and total genomic DNA. Padlock probes offer highly specific detection of short target sequences by combining detection by ligation and signal amplification. In this approach only genes in sequences containing strand breaks, which become single-stranded in the tail, are available for hybridisation. Thus the total number of signals from the padlock probes per comet gives a direct measure of the amount of damage (strand-breaks) present and allows the repair process to be monitored. This method could provide insights on the organisation of genomic DNA in the comet tail. Alu repeat containing DNA was repaired rapidly in comparison with total genomic DNA, and the studied genes were generally repaired more rapidly than the Alu repeats.
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PMID:Study of gene-specific DNA repair in the comet assay with padlock probes and rolling circle amplification. 2131 12